Conventionally, cigarette filters are mostly manufactured from tows of cellulose ester fibers. From within these, since cellulose acetate fiber tows can maintain the rod shape in which they are deposited using triacetin which is a solvent thereof, it is possible to process filters easily, and they have the advantage of being usable in paper rolling cigarette manufacturing machines of high operating speeds.
After smoking, as cigarette stubs, filters are generally withdrawn by means of disposal in ash trays, or refuse bins, however, depending on the situation, by being thrown away, they can be left in natural environments, such as fields and mountains, rivers, lakes, and seas, and on roadways.
However, after smoking, the filter portion of the cigarette stub maintains a rod-like shape and this shape does not break down, in addition, since the tipping paper of the filter portion is hard to peel off, and the decomposition of the cellulose acetate fiber itself which is used in the filter is slow, and the like, it is difficult for the shape of the filter portion of the cigarette stubs in the natural environment to break down. Consequently, the leaving of these types of cigarette filters in the natural environment is a cause of the problem of environmental pollution, and this is also becoming a societal problem.
With regard to this type of problem, Japanese Patent Application, First Publication, No. Hei 6-49275 proposes a method of obtaining cellulose acetate which is superior in its decomposition properties by means of manufacturing cellulose acetate using sulfuric acid catalyst, and wherein the ratio of the amount (a) of sulfuric acid which remains in the cellulose acetate to the amount (b) of alkaline (earth type) metals contained in the cellulose acetate, (b)/(a), is 0.1-1.
In addition, in order to raise the biodegradability of cellulose acetate fiber, the inclusion of specific chemical compounds in the cellulose acetate fiber has been proposed. As this type of chemical compound, for example, nitrogen containing compounds are proposed in Japanese Patent Application, First Publication, No. Hei 7-99959, starch compounds are proposed in PCT Application, Japanese Publication, No. Hei 7-500385, and starch acetates are proposed in Japanese Patent Application, First Publication, No. Hei 6-329832. However, there is the problem that it is difficult to mix these compounds with cellulose acetate.
In addition, methods of coating or impregnating cellulose acetate fibers which are used in cigarette filters with various plasticizing agents are already known. For example, methods for impregnation with dicarboxylic acid, polycarboxylic acid and their anhydrides, and propionic acid polyethylene glycol, triethyleneglycol diacetate, and the like are disclosed in Japanese Patent Application, First Publication, No. Hei 2-39873; methods for impregnation with glycerin compounds are disclosed in PCT Application, Japanese Publication, No. Sho 63-500422; methods for impregnation with diacetate of polyethylene glycol are disclosed in Japanese Patent Application, First Publication, No. Sho 60-98978; methods for impregnation with polyalkylene glycol are disclosed in U.S. Pat. No. 4,752,348; methods for coating with fatty acid glycerin esters are disclosed in Japanese Patent Application, First Publication, No. Sho 59-227289; methods for coating with polyalkylene oxide are disclosed in U.S. Pat. No. 5,453,144, and methods for impregnation with lower fatty acid esters of multivalent alcohols, polyethylene glycol, and the like are disclosed in Japanese Patent Application, First Publication, No. Hei 7-76632.
However, in these methods, the function of the plasticizing agents is mainly to form a three dimensional network structure by the mutual bonding of the fibers by dissolving the surface of the cellulose acetate fibers, and while making a filter form which can be maintained, a suitable hardness is given to the filter. That is to say, in the above methods, the coating and impregnation of the cellulose acetate fiber with plasticizing agents was not for the purpose of the decomposition of fibers, rather it was for the purpose of controlling the decomposition of the fibers so as to make it possible to stably maintain the shape of the filter for a long period.
In addition, since the plasticizing agent coating or impregnating the surface of the fiber comes into direct contact with the cigarette smoke, it effects the smoking flavor. Consequently, the amount of the plasticizing agent used is usually 3-10% by weight since the quality of the filter is degraded by the occurrence of excessive dissolution and fusion of the cellulose acetate fibers when the amount is too great.
Furthermore, outside of the field of cigarette filters, for example, Japanese Patent Application, First Publication, No. Hei 4-126817, and Japanese Patent Application, First Publication, No. Hei 6-146109 propose cellulose acetate fibers which have improved deep dyeing properties by the addition of polypropylene glycol, polyethylene glycol and the like to cellulose acetate fibers. However, since these proposals are both related to cellulose acetate fibers for use as clothing fibers, they teach nothing at all about increasing the decomposability of filter materials or, specifically, cigarette filters.
Objects of the present invention are to increase the decomposability of cellulose acetate fibers in the natural environment, and to make the break down of the shape of the fibers of filter materials and the shape of cigarette filters easier.